Electric discharge tube with luminescent substance coating



y 1956 KARL AKE GERHARD BJURKMAN 2,748,306

ELECTRIC DISCHARGE TUBE WITH LUMINESCENT SUBSTANCE COATING Filed June 5, 1951 ATTORNEY A United States Patent ELECTRIC DISCHARGE TUBE WITH LUMI- NESCENT SUBSTANCE COATENG Karl like Gerhard Bjiirkman, Hammarbyhojden, Sweden,

assignor to Lumalampan Aktiebolag, Stockholm, Sweden, a corporation of the Kingdom of Sweden Application June 5, 1951, Serial No. 229,898

Claims. (Cl. 313-109) This invention relates to an electric discharge tube with luminescent substance coating, which also means such tubes, in which the luminescent substance can be contained in the tube wall itself.

This invention is based on the observation that tube ends as compared with the portion between the electrodes of the tube form somewhat darker portions. Certainly the discharge at low pressure filling is of difiuse character, so that it extends also to the space behind the electrodes; but it cannot be avoided that without special arrangement the electrode spaces contrast with the remainder of the tube.

According to this invention, it is suggested that the insulating pieces surrounding the electrode lead-in wires should be covered with a UV-refiecting coating. Preferably this coating may consist of metal oxide, especially a white one, such as magnesium oxide, aluminium oxide or zirconium oxide. Other white oxides may also be used, but it seems that those proposed also are accompanied by a certain gettering efiect, which will be further discussed below.

The short-wave ray emanating from the discharge illuminates the coating applied to the insulating pieces and is reflected by the same out through adjoining parts of the luminescent coating of the tube. In this way the tube ends can thus be made to emit light with approximately the same intensity as the main part of the tube. It may be mentioned that application of a UV-transforming luminous powder will not at all to the same degree eliminate the contrast between the end parts of the tube and its main portion. Certainly, visible light pases through the tube end, emanating from the luminophorous coating applied to the insulating pieces, but elimination of the contrast efiect will be much more complete, if reflected UV-light is made to radiate upon the luminophorous coating on the end part of the tube envelope.

That a certain getter effect exists could among others be ascertained by the fact that the usual darkening of the luminophorous layer near the electrodes was considerably reduced and delayed. An increase of the getter effeet can be obtained by adding to the UV-reflecting coating a getter of the usual type, for instance a metallic one such as zirconium or magnesium.

The invention is illustrated by two examples of design as shown in the accompanying drawing.

Fig. 1 shows a discharge tube 1 with luminescent coating 2 on the inside of the tube. Each electrode 3 is supported by a lead-in wire 5, fused into lamp feet 4. To the lamp foot is applied a UV-reflecting coating 6, as per invention.

Fig. 2 shows a discharge tube, in which electrodes 3 and 7, fitted with lead-in wires 5 and 8, respectively, are fused together into a lamp foot 4. The lead-in wires 8 are extending into the lamp so that electrode 7 is situated near the top of tube envelope 1. The lead-in wires 8 are surrounded by an insulating glass tube 9 or similar. Lamp foot 4 as well as insulation 9 are covered by a UV-refleeting coating 6 and 10, respectively.

What I claim is:

l. A gaseous electric discharge lamp comprising a light transmitting envelope coated with a luminescent material and having an electrode disposed at each end of the envelope, each of said electrodes being provided with a foot within and connected with the envelope and with at least one lead-in wire, said foot extending along and around the lead-in wire within the envelope but not around the electrode and being coated with a UV-reflecting coating consisting of a metal oxide.

2. Electric discharge lamp as defined in claim 1 in which the UV-reflecting coating consists of a white metal oxide.

3. Electric discharge lamp as defined in claim 2 in which the white metal oxide coating comprises an oxide of a metal of the class consisting of magnesium, aluminum and zirconium.

4. Electric discharge lamp as defined in claim 1 in which a metallic getter substance is added to the metal oxide coating.

5. Electric discharge lamp as defined in claim 4 in which the metallic getter comprises a metal of the class consisting of magnesium and zirconium.

References Cited in the file of this patent UNITED STATES PATENTS 292,403 Beeman Ian. 22, 1884 299,885 Welsh June 3, 1884 2,346,522 Gessel Apr. 11, 1944 2,440,832 Pennybacker May 4, 1948 2,445,692 Porter July 20, 1948 2,457,503 Singer Dec. 28, 1948 

1. A GASEOUS ELECTRIC DISCHARGE LAMP COMPRISING A LIGHT TRANSMITTING ENVELOPE COATED WITH A LUMINESCENT MATERIAL AND HAVING AN ELECTRODE DISPOSED AT EACH END OF THE ENVELOPE, EACH OF SAID ELECTRODES BEING PROVIDED WITH A FOOT WITHIN AND CONNECTED WITH THE ENVELOPE AND WITH AT LEAST ONE LEAD-IN-WIRE, SAID FOOT EXTENDING ALONG AND AROUND THE LEAD-IN-WIRE WITHIN THE ENVELOPE BUT NOT AROUND THE ELECTRODE AND BEING COATED WITH UV-REFLECTING COATING CONSISTING OF A METAL OXIDE. 